Scratch

I recommend downloading the project that you want to use the scripts from, then selecting the sprite who has the script, then inside of Scratch click the "export sprite" button. Finally, in the project that you are making, click the folder button that is under the stage to get a sprite from a file, and import the sprite that you just saved.

Paulmedwal

Here's what I did to solve the problem you mention:

I went to one of my old projects and exported a sprite I'd made (that had 6 scripts associated with it) to the "Things" folder.

Then I opened a New project.  It had the cat sitting there, so I clicked to get another sprite from a folder.  I chose the Things folder and chose my old sprite.

So now I had the cat and my old sprite on the screen. (And the old sprite had its 6 scripts with it.) 

Now I clicked on my old sprite, then clicked on Costumes.  And now you have a choice: you can "paint" a new costume for the sprite, or you can "import" an already existing sprite from Scratch, like the basketball.

If you import the basketball (so the cat can play with it) you can then delete each of the OLD costumes that the sprite had.  In my case, the old sprite I had imported to get its scripts had 14 costumes with it!!  I added the basketball and then carefully deleted each of the 14 old costumes.  So now I had the basketball with the 6 scripts.

Done.